How the elements get along: sand falls and piles up, and being heavy it sinks straight through water and oil. Water flows and levels out, and instantly quenches any fire it touches into steam. Oil floats on top of water and burns fiercely — one spark and the whole slick goes up. Fire lives briefly, licks upward, puffs out smoke and spreads to anything flammable. Plants stand still but slowly drink neighbouring water to grow — and they burn too. Smoke drifts up and fades; steam does the same but sometimes condenses back into a drizzle of water. Acid is the bully: it dissolves sand, plants, oil and smoke, using itself up as it eats — only walls (and water) can stop it. Walls are yours to build: draw basins, funnels and shelves, then knock holes in them with the eraser.